Mesoporous activated carbon and methods of producing same

ABSTRACT

Mesoporous activated carbon is disclosed. In at least some embodiments, virgin activated carbon to be processed may be coconut shell-based. The enhanced activated carbon may have a mesopore structure of at least about 10%. The enhanced activated carbon may be produced through a calcium-catalyzed activation process. A chelator may also be used. Catalyzed thermal activation may be carried out until a desired mass loss is achieved.

FIELD OF THE TECHNOLOGY

One or more aspects relate generally to activated carbon. Moreparticularly, one or more aspects relate to mesoporous activated carbonand methods of producing the same.

BACKGROUND

Activated carbon is widely used in gas purification, water purification,metal extraction, and sewage treatment among other applications.Activated carbon is generally a form of carbon that has been physicallyor chemically processed to increase its porosity and surface areaavailable for adsorption and chemical reactions. Powdered activatedcarbon (PAC) and granular activated carbon (GAC) are among common forms.

SUMMARY

Aspects relate generally to activated carbon and various techniques forproducing mesoporous activated carbon.

In accordance with one or more embodiments, a method of producing anenhanced activated carbon may comprise providing a predominantlymicroporous virgin activated carbon, introducing an aqueouscalcium-based catalyst to the virgin activated carbon to produce acatalyst impregnated activated carbon, and heating the catalystimpregnated activated carbon at a pyrolysis temperature until a mesoporevolume of at least about 10% is achieved while substantially maintaininga micropore structure associated with the virgin activated carbon toproduce the enhanced activated carbon.

In some embodiments, the method may be associated with a mass loss of atleast about 10%. The aqueous calcium-based catalyst may comprise calciumchloride. The aqueous calcium-based catalyst may comprise a chelator. Insome embodiments, the chelator may comprise citric acid. In at leastsome embodiments, the virgin activated carbon is coconut shell-based. Insome embodiments, the virgin activated carbon is at least about 90%microporous. The catalyst impregnated activated carbon may be maintainedat an intermediate temperature prior to reaching the pyrolysistemperature. The virgin activated carbon may be sprayed with or soakedin the aqueous calcium-based catalyst. In some embodiments, the methodmay further comprise oxidizing the catalyst impregnated activated carbonwith carbon dioxide. In other embodiments, the catalyst impregnatedactivated carbon may be oxidized with carbon dioxide and steam.

In accordance with one or more embodiments, a method of producing anenhanced activated carbon may comprise providing a spent activatedcarbon having a calcium content of greater than or equal to about 0.5%by weight, and heating the spent activated carbon to a pyrolysistemperature until a mesopore volume of at least about 10% is achieved toproduce the enhanced activated carbon.

In some embodiments, the spent activated carbon is predominantlymicroporous. The spent activated carbon may be coconut shell-based. Themethod may further comprise oxidizing the spent activated carbon with atleast one of carbon dioxide and steam.

In accordance with one or more embodiments, a method of facilitatingwater treatment may comprise providing a vessel containing coconutshell-based activated carbon having a mesopore volume of at least about10%, and fluidly connecting a source of water to the reactor fortreatment via contact with the coconut shell-based activated carbon.

In some embodiments, the method may further comprise reactivating thecoconut shell-based activated carbon after a predetermined time period.

In accordance with one or more embodiments, a coconut shell-basedactivated carbon may comprise a mesopore volume of at least about 10%.

In some embodiments, the coconut shell-based activated carbon may havean apparent density of about 0.43 glee to about 0.49 g/cc. In otherembodiments, the coconut shell-based activated carbon may have an iodinenumber of about 1100 mg/g.

Still other aspects, embodiments, and advantages of these exemplaryaspects and embodiments, are discussed in detail below. Moreover, it isto be understood that both the foregoing information and the followingdetailed description are merely illustrative examples of various aspectsand embodiments, and are intended to provide an overview or frameworkfor understanding the nature and character of the claimed aspects andembodiments. The accompanying drawings are included to provideillustration and a further understanding of the various aspects andembodiments, and are incorporated in and constitute a part of thisspecification. The drawings, together with the remainder of thespecification, serve to explain principles and operations of thedescribed and claimed aspects and embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of at least one embodiment are discussed below withreference to the accompanying figures. The figures are provided for thepurposes of illustration and explanation and are not intended as adefinition of the limits of the invention. In the figures:

FIGS. 1-8 present data referenced in the accompanying Examples.

DETAILED DESCRIPTION

In accordance with one or more embodiments, an activated carbon may betreated to increase its mesopore volume while retaining its inherentmicropore structure. The enhanced mesopore structure may provideimproved adsorption kinetics and adsorption capacity for largermolecular weight compounds. The intact micropore structure may providevolatile organic compounds (VOC) adsorption capacity. The modified porestructure of the activated carbon material may lead to longer bed lifebetween carbon exchanges, and lower life cycle costs. The enhancedactivated carbon may conform to various industry defined physical andperformance requirements for various applications, such as leachabilityfor potable water production. The enhanced activated carbon may providetrace VOC removal capacity and adsorptive performance to remove taste,odor, and other organic contaminants. The enhanced activated carbon maybe subsequently reactivated.

In accordance with one or more embodiments, the activated carbon may bepowdered activated carbon (PAC) or granular activated carbon (GAC). Anactivated carbon material which is predominantly microporous instructure may be chemically treated and/or thermally modified toincrease its mesopore volume. In at least some embodiments, any startingmaterial that has a micropore volume of at least about 90% may betreated to increase its mesopore volume. Such treatment may result in nosignificant loss of micropore structure although the relative percentageof micropore volume with respect to total pore volume may be altered. Asa result, during adsorption the transport rate of organic contaminantsinto the micropores may be increased and/or less hindered by competingadsorbates such as natural organic matter. In some non-limitingembodiments, a starting material may be more than about 95% microporousin volume. In some non-limiting embodiments, a starting material may beless than about 5% mesoporous. In other embodiments, a starting materialmay be less than about 10% mesoporous. In still other embodiments, astarting material may be less than about 20% mesoporous.

The mesopore volume of an activated carbon treated in accordance withone or more non-limiting embodiments may be increased. In someembodiments, enhanced activated carbon may have a mesopore volume of upto about 10%. Thus, in some non-limiting embodiments, mesopore volumemay be increased from less than about 5% to up to about 10%. In otherembodiments, enhanced activated carbon may have a mesopore volume of upto about 20%. In at least some embodiments, treated activated may have amesopore volume of up to about 30%. For purposes of one or moredisclosed embodiments, the term micropore refers to a pore of about 2 toabout 20 Angstroms in diameter while the term mesopore refers to a poreof about 20 to about 500 Angstroms in diameter based on definitionscommonly known to those skilled in the art and as adopted by theInternational Union of Pure and Applied Chemistry (IUPAC). Percentagesrelating to micropore volume and mesopore volume, or percentages inconjunction with the terms microporous and mesoporous, used above andthroughout may generally refer to percentage of total pore volume ascalculated from gas adsorption isotherms and as commonly recognized bythose skilled in the art.

Any predominantly microporous activated carbon may be treated to enhanceits performance. In some embodiments, a starting material to be enhancedmay be virgin activated carbon. In other embodiments, a startingmaterial may be spent activated carbon which has been used for treatmentand may have reached its adsorption capacity. In some non-limitingembodiments, spent activated carbon used as a starting material may havea calcium content of greater than or equal to about 0.5% by weight. Inother non-limiting embodiments, spent activated carbon used as astarting material may have a calcium content of greater than or equal toabout 1% by weight. In at least one embodiment, the starting materialmay have already undergone at least one physical or chemical treatmentprocess, for example, as in the case of a virgin activated carbon. Inother embodiments, the starting material may not have undergone previoustreatment. In accordance with one or more embodiments, an enhancedactivated carbon such as a mesoporous activated carbon may be producedfrom various carbonaceous source materials including nutshells, peat,wood, coir, lignite, coal, and petroleum pitch. In some embodiments, thestarting material may be coconut-shell based. In some non-limitingembodiments, an enhanced activated carbon may be a coconut shell-basedactivated carbon. In at least one embodiment, Westates® coconutshell-based granular activated carbon (AquaCarb®830C, 1230C and 1230AWC)commercially available from Siemens Industry, Inc. (Warrendale, Pa.) maybe treated and enhanced. In some embodiments, the starting material maybe less than about 10% mesoporous. In at least some embodiments, thestarting material may be less than about 5% mesoporous. In someembodiments, the starting material may have at most about 1% to about 5%mesoporous volume and about 95% to about 99% microporous volume. In atleast some non-limiting embodiments, the starting material may be about95% microporous and about 5% mesoporous.

In accordance with one or more embodiments, an enhanced activated carbonmay have a mesopore volume of about 5% to about 50% with the balancebeing substantially microporous. In at least some embodiments, themesopore volume may be about 10% to about 30% with the balance beingsubstantially microporous. In still other embodiments, the mesoporevolume may be about 15% to about 25% with the balance beingsubstantially microporous. There may be macropores or other porestructures, such as those having a diameter of greater than about 500Angstroms, in addition to the mesopores and micropores but they are notbelieved to measurably influence performance of the activated carbon. Insome embodiments, enhanced coconut shell-based activated carbons mayoffer the benefits of traditional coconut shell-based activated carbons,as well as the benefits of bituminous coal based carbons. In at leastone or more embodiments, any lignocellulosic material may be used as anatural source of microporous activated carbon starting material.

In accordance with one or more embodiments, the rate of activation of astarting material may be increased. In some non-limiting embodiments, anactivated carbon starting material may be oxidized and/or gasified toincrease its porosity. In at least one embodiment, treatment of anactivated carbon starting material may be catalyzed. Thermal activationmay be catalyzed to increase the rate of activation. Various catalystsmay be used to catalyze the rate of activation. In some embodiments, ametal catalyst may be used. In at least some embodiments, a transitionmetal catalyst may be used. In one non-limiting embodiment, the rate ofactivation may be calcium-catalyzed. Various sources of calcium, such ascalcium chloride, calcium acetate and calcium propionate may be used. Inaccordance with one or more embodiments, a catalyst may be present insolution for application to a starting material. Any solvent may beused. In some preferred embodiments, an aqueous solvent may be used.

In some non-limiting embodiments, a catalyst may already be present in amaterial to be treated, such as in spent activated carbon which may betreated for reactivation purposes. The catalyst may be present due toprevious activation or due to prior use in the treatment of a processstream. Carbon reactivation may offer environmental benefits, minimizingwaste by recycling and reusing spent carbon. Thermal or chemicalreactivation may restore the surface area and pore volume of spentcarbon to a point close to that of a virgin carbon. The process ofcarbon reactivation may be very similar to the process of treatingvirgin activated carbon. Reactivated carbons in accordance with one ormore embodiments may provide a cost-effective alternative to virgincarbon while providing excellent performance in various treatmentapplications. In some embodiments, a spent activated carbon which has orpreviously had a desired mesopore volume may be reactivated. In otherembodiments, a spent activated carbon that was not previously enhancedto exhibit a desired mesopore volume may be reactivated to produce anenhanced activated carbon having the desired mesopore volume.

In accordance with one or more embodiments, a chelator may beimplemented. In some embodiments, a catalyst may be introduced using achelator. In at least one embodiment, the catalyst source, such ascalcium chloride for example, may be impregnated with a chelator. Ingeneral, any soluble chelator may be used. In at least one non-limitingembodiment, citric acid may be used as a chelator. In other non-limitingembodiments, EDTA or another known chelator may be used. In at leastsome non-limiting embodiments, no chelator is used.

In accordance with one or more embodiments, a catalyst may aid oxidanttransfer to a surface of the activated carbon. Carbon monoxide may beproduced by uncatalyzed gasification of oxidation by steam. A metalcatalyst precursor may convert to an active oxide, such as a metal oxideor a transition metal oxide, via reaction with carbon dioxide and/orsteam. Carbon dioxide may be generated from steam and carbon monoxidevia the gas phase water-gas shift reaction. The oxidant may diffuse tothe interior of the activated carbon grain and chemisorb to metal oxidecrystallites. The oxidant may diffuse to the metal oxide-carboninterface and to a free active carbon site. Solid carbon-oxygenfunctional groups may gasify to form carbon monoxide. The gasificationprocess may be associated with mass loss via void formation that mayresult in increased mesopore volume. The dispersion of the oxide maycontrol the resulting crystallite size. For example, if the calcium isnot dispersed well in the activated carbon, the oxidation may take placeat only a few sites resulting in an overly focused burn-off. When welldispersed, the result of the oxidation is also well dispersed and manyrelatively small mesopores are created rather than a few relativelylarger mesopores. Oxidant transfer may occur most rapidly at thecrystallite sites and is therefore not available to more slowly oxidizenoncatalytic areas or surfaces. Without the catalyst, burn-off may berelatively slow and result only in new micropore volume.

In accordance with one or more embodiments, an aqueous catalyst solutionmay be applied to a starting material. In some embodiments, the startingmaterial may be soaked in the aqueous catalyst solution. In otherembodiments, the starting material may be sprayed with the aqueouscatalyst solution. Concentration of the aqueous catalyst solution may beadjusted based on the application method. For example, in somenon-limiting embodiments, starting material may be sprayed with acatalyst solution having a chelator concentration of about 5% to about30% or greater by weight. In some non-limiting embodiments, the chelatorconcentration of a sprayed catalyst solution may be about 15%. In othernon-limiting embodiments, starting material may be soaked in a catalystsolution having a chelator concentration of about 3% to about 15% byweight. In some non-limiting embodiments, the chelator concentration ofa catalyst solution in which starting material is soaked may be about7%. In some embodiments, the chelator may facilitate distribution of thecatalyst.

In accordance with one or more embodiments, the starting material mayhave undergone a physical or chemical pretreatment prior to catalysis.In other embodiments, no pretreatment may have occurred. The aqueouscatalyst solution may include a source of a catalyst, such as calciumchloride. A chelator, such as citric acid, may also be present. Thecatalyst may be impregnated with the chelator. The starting material maybe sprayed with or soaked in the aqueous catalyst solution for apredetermined period of time. In some embodiments involving soaking, thestarting material may be soaked in the catalyst solution for about 1hour to about 24 hours. In some non-limiting embodiments, the startingmaterial may be soaked for about 12 hours. The liquid may then beremoved, such as by vacuum filtration.

The catalyzed material may then be heated up to a pyrolysis temperature.The pyrolysis temperature may depend on the material to be treated. Insome embodiments, the pyrolysis temperature may be at least about 600°C. In some embodiments, a pyrolysis temperature of about 600° C. toabout 1200° C. may be used, In some specific non limiting embodiments, apyrolysis temperature of about 800° C. to about 1100° C. may be used. Inat least some non-limiting embodiments, a temperature of about 900° C.to about 1000° C. may be used. The heating may be staged such that oneor more intermediate temperatures is achieved prior to reaching thepyrolysis temperature. An intermediate temperature may be maintained fora predetermined period of time prior to further heating. Parameters andconditions associated with one or more intermediate temperatures mayvary. In some embodiments, the catalyzed material may be heated insteam, carbon dioxide, nitrogen, or mixtures of the gases during a firstheating stage. The catalyzed material may then be heated in nitrogen,carbon dioxide and/or steam during a second heating stage. In otherembodiments, a single heating stage involving steam, carbon dioxideand/or nitrogen may be implemented. In some specific non-limitingembodiments, carbon dioxide may be used as a sole oxidant. In otherspecific non-limiting embodiments, carbon dioxide in conjunction withsteam may be used as oxidant.

Heating at the pyrolysis temperature may continue until a desired massloss is achieved, such as about 5% to about 30%. A degree of mass lossmay depend on a desired ratio of micropore and mesopore volume asfurther mass loss in the presence of the catalyst will produceadditional mesopore volume thus reducing the total fraction of microporevolume. Thus, during enhancement, the percentage of mesopore volume mayincrease and the percentage of micropore volume may decrease as afunction of total pore volume while still preserving the microporestructure and enhancing the mesopore structure of the carbon material.In some non-limiting embodiments, mass loss of about 10%, 20%, 30%, 40%or 50% may be achieved. Upon achieving a pyrolysis temperature, massloss may be a function of treatment time and oxidant addition, forexample, the mass of steam and/or carbon dioxide per mass of activatedcarbon per time. In some specific non-limiting embodiments, a residencetime of about two hours in a kiln with 1 pound of steam per pound of GACper hour may be used. To maintain integrity of the particles, mass lossmay be generally limited to about 20% in some embodiments. In at leastone non-limiting preferred embodiment, mass loss of about 10% may beachieved. The resulting treated activated carbon may then be cooled,preferably rapidly, with steam and/or nitrogen flow. In somenon-limiting preferred embodiments, steam may be used for cooling.

In accordance with one or more embodiments, the metal catalyst may serveto increase the rate of carbon gasification by increasing oxidanttransfer to the activated carbon surface. The catalyst does not act in atraditional manner in that it does not lower the activation energyrequired for gasification. At activation temperatures the organicchelator is oxidized and gasifies from the carbon surface as an organiccontaminant does typically at reactivation temperatures. The chelatorfacilitates achieving a sufficient concentration and homogeneousdistribution of metal catalyst within the activated carbon, such thatthe catalyst is at a level to sufficiently aid gasification. Thecatalyst may remain in the enhanced activated carbon product and futurereactivation of the material may be adjusted to limit any excessivegasification of the material.

In accordance with one or more embodiments, a mesoporous activatedcarbon material may be associated with a specified mesh size. Somenon-limiting mesh size examples for the mesoporous activated carbonproduct include 8 by 30, 12 by 30 and 12 by 40. An effective size of themesoporous activated carbon product may also vary. Some non-limitingexamples are about 0.8 mm to about 1.1 mm, about 0.6 mm to about 0.85 mmor about 0.55 mm to about 0.75 mm. Some non-limiting examples ofenhanced activated carbons may have an iodine number of about 1100 mg/g.Some non-limiting examples of enhanced activated carbons may becharacterized by an apparent density of about 0.43 g/cc to about 0.49glee. Some non-limiting examples of enhanced activated carbons may becharacterized by a hardness of about 95. Some non-limiting examples ofenhanced activated carbons may be characterized by an abrasion rating ofabout 85. Some non-limiting examples of enhanced activated carbons maybe associated with a contact pH level of about 9 to about 10.

In accordance with one or more embodiments, mesoporous activated carbonmay be used for organic contaminant removal. In some embodiments, themesoporous activated carbon may be implemented in any aqueous-phaseapplication. Mesoporous activated carbon may be implemented in afluidized bed associated with a liquid or vapor phase carbon treatmentsystem. Disinfection byproducts and precursors thereof, as well astastes and odors, may be removed from surface water. High performanceVOC removal in groundwater sources may also be accomplished. Bulkorganic and total organic carbon removal may also be facilitated.

In at least certain embodiments, the mesoporous activated carbon may beused in those applications where contact time is limited or a highbackground total organic carbon (TOC) concentration exists. In somenonlimiting embodiments, halogenated organics such as trihalomethanesmay be removed. In at least one nonlimiting embodiment, chloroform maybe removed. Tastes and odors, pesticides, polycyclic aromatichydrocarbons, polychlorinated biphenyls, endocrine disruptors,pharmaceuticals and personal care products may all be treated withmesoporous activated carbon in accordance with one or more non-limitingembodiments.

In accordance with one or more non-limiting embodiments, wastewater maybe contacted with enhanced activated carbon in GAC form in a semi-batchor continuous process. In some non-limiting embodiments, fixed bed,expanded bed, moving bed or fluidized bed adsorption processes may beused in conjunction with the enhanced activated carbons discussedherein. Various factors may impact contactor design including particlesize, column diameter, flow rate of incoming wastewater, residence time,adsorption bed height, pressure drop and breakthrough time. In general,as the wastewater moves through the enhanced activated carbon,pollutants may be adsorbed via movement from the wastewater to thecarbon bed. The overall adsorption process may be dominated by a masstransfer step from the wastewater bulk to the surface of the carbonparticle through the boundary layer surrounding the particle. Internaldiffusion through the carbon pores and adsorption onto the surface ofthe particle may also be involved. In other non-limiting embodiments,enhanced activated carbon in PAC form may be introduced in bulk to asolution for treatment. PAC may generally be associated with a smallerparticle size and may be added directly to other process units such asraw water intakes, rapid mix basins, clarifiers and gravity filtersrather than being used in a dedicated adsorber vessel.

The function and advantages of these and other embodiments will be morefully understood from the following examples. The examples are intendedto be illustrative in nature and are not to be considered as limitingthe scope of the systems and methods discussed herein.

Example 1

Mesoporous coconut shell-based activated carbon was produced inaccordance with one or more embodiments. About 8 g to about 12 g ofcoconut shell-based activated carbon was treated. More specifically,about 9 g to about 11 g of coconut shell-based activated carbon wastreated. About 0.1% to about 5% w/w Ca was used to catalyze the coconutshell-based activated carbon. More specifically, about 0.5% to about2.0% w/w Ca was used. About 0.15 gal/lb GAC to about 0.3 gal/lb GAC wasused. Specifically, about 0.2 gal/lb GAC to about 0.25 gal/lb GAC may beused.

The following specific materials were used:

-   -   10 g AquaCarb1240C® granular activated carbon, (2% moisture).    -   Citric Acid (anhydrous)    -   Calcium Chloride (anhydrous)

The following assumptions and principles were used:

-   -   AC1240C® granular activated carbon was mixed with 1% w/w Ca,    -   0.225 gal solution/lb GAC.

The following calculations were used:

Mass of CaCl₂

${\left( \frac{10\; g\; {GAC}}{batch} \right)\left( \frac{0.01g\mspace{11mu} {Ca}}{g\mspace{11mu} {GAC}} \right)\left( \frac{1\; {mol}\mspace{11mu} {Ca}}{40.08\; g\mspace{11mu} {Ca}} \right)\left( \frac{1\; {mol}\mspace{14mu} {CaCl}_{3}}{1\; {mol}\mspace{11mu} {Ca}} \right)\left( \frac{110.98g\mspace{11mu} {CaCl}_{2}}{{mol}\mspace{11mu} {CaCl}_{2}} \right)} = {0.28g\mspace{11mu} {CaCl}_{2}}$

Mass of C₈H₈O₇

${\left( \frac{10\mspace{11mu} g\mspace{11mu} {GAC}}{batch} \right)\left( \frac{0.01g\mspace{11mu} {Ca}}{g\mspace{11mu} {GAC}} \right)\left( \frac{1\; {mol}\mspace{11mu} {Ca}}{40.08\mspace{11mu} g\mspace{11mu} {Ca}} \right)\left( \frac{2\; {mol}\mspace{11mu} C_{6}H_{8}O_{1}}{1\; {mol}\mspace{11mu} {Ca}^{2 +}} \right)\left( \frac{192.12\; g\mspace{11mu} C_{6}H_{8}O_{7}}{{mol}\mspace{11mu} C_{6}H_{8}O_{7}} \right)} = {0.96\; g\mspace{11mu} C_{6}H_{8}O_{7}}$

Volume of H₂O

${\left( \frac{10\; g\mspace{11mu} {GAC}}{batch} \right)\left( \frac{1\mspace{11mu} {lb}}{454\mspace{14mu} g} \right)\left( \frac{0.225\mspace{11mu} {gal}}{lb} \right)\left( \frac{3785\mspace{11mu} {mL}}{gal} \right)} = {18.8\mspace{11mu} {{mL}.}}$

GAC was soaked in solution for about 12 hours. Liquid was then removedby vacuum filtration. Without drying, material was heated to about 300°C. in N₂ (approximately 17 cc/min/g GAC) (or similarly inertatmosphere). With N₂ flow continuing, the GAC was heated in steam (0.01to 0.2 mL/min/g GAC) from 300° C. to pyrolysis temperature (about 800°C. to about 1000° C.), Heating at pyrolysis temperature was continueduntil a desired mass loss was achieved, typically 10% as a minimum and15% as an optimum. In some embodiments, maximum may be about 30% asparticles lose integrity. In some embodiments, mass loss rate maylargely be dependent upon the steam rate. The material was then cooledas rapidly as possible with steam/N₂ flow continuing.

Discrete data relating to pore volume distribution for activated carbonproduced in accordance with one or more embodiments disclosed herein ispresented in FIG. 1. Bituminous relates to F400 activated carbon,commercially available from Calgon®, which generally has fewermicropores and significantly more mesopores than the AquaCarb1240C®starting material used in this Example. Reactivated Coconut relates to aspent coconut shell-based activated carbon that was commerciallyreactivated. Mesoporous Coconut and Mesoporous React. Coconut relate toactivated carbon produced with one or more of the embodiments disclosedherein. Corresponding cumulative data relating to pore volumedistribution is presented in FIG. 2. FIGS. 1 and 2 were produced fromargon adsorption isotherms where the isotherm data has been reducedusing the density functional theory (DFT). Both the cumulative anddiscrete representations of the pore volume indicate that mesopores wereformed in the activated carbon during treatment as per the embodimentsdisclosed herein while micropore volume was mostly maintained duringthose treatments.

Example 2

A target application is removal of disinfection by-products from treateddrinking water and as such chloroform can be used to represent thelarger class of trihalomethanes. Rapid small-scale column tests (RSSCTs,ASTM D6586) were performed to assess chloroform removal performance ofthe GAC produced in accordance with one or more of the disclosedembodiments, For these RSSCTs, chloroform was spiked to a level of 90μg/L in a natural groundwater; RSSCTs were scaled to represent afull-scale bed operating at a 5 minute empty-bed contact time using12×40 US mesh full-size grains. Effluent chloroform concentrations weremeasured for about 16,000 bed volumes, corresponding to approximately 2months of full-scale service.

FIG. 3 presents chloroform breakthrough data in the groundwater asmeasured in RSSCTs. The results indicate that the mesoporous activatedcarbon produced in accordance with one or more embodiments provided 40%longer bed life than the virgin material and about 65% longer bed lifethan the F400 product in a natural groundwater containing competingbackground organics at a level of 0.5 mg/L TOC.

Example 3

Mesoporous coconut shell-based activated carbon was produced with a soakmethod in accordance with one or more embodiments, 192.5 gallons of 50%w/w citric acid solution was added to 2729 gallons of water. 80 gallonsof 32% w/w CaCl2 was added to the citric acid/water solution. Theresulting solution was then added to 10,000 lb virgin 12×30 US Meshgranular coconut shell-based activated carbon. The activated carbon wasallowed to soak in the solution for 12 hours. The solution was thendrained from the activated carbon. The activated carbon was heated to950° C. in the presence of steam at an application rate of 11b steam/lbactivated carbon.

Mesoporous coconut shell-based activated carbon was separately producedwith a spray method in accordance with one or more embodiments. 74 mL of50% w/w citric acid solution was added to 222 mL of water to produce15.6% w/w citric acid solution. 13.2 g CaCl2 was added to the 15.6% w/wcitric acid solution. 98.7 g of the resulting solution was applied as afine mist to a 1 mm thick layer of 307 g virgin 12×40 US Mesh granularcoconut shell-based activated carbon. The activated carbon was thendried for 1 at 32° C. and then heated to 100° C. for 1 hr. Thetemperature was then ramped to 930° C. and held for 1 hr. The activatedcarbon was cooled in steam to room temperature.

Example 4

RSSCTs were conducted for the removal of 2-methylisoborneol (MIB) fromclarifier effluent at a drinking water treatment utility. These testssimulated the full-scale operation of existing GAC beds at the treatmentfacility (Table 1). RSSCT test operation was based on ASTM MethodD-6586.

TABLE 1 Dimensions and operating parameters for RSSCTs. Full-ScaleSmall-Scale Influent MIB 120 ng/L, max 125 ng/L Bed Depth 54 in 2 cmFlow 1.5 mgd 6-10 mL/min Area 365 ft2 0.32 cm2 EBCT 11.8 min 3.6 s GrainSize  8 × 30 (1.49) US Mesh (mm) 170 × 200 US Mesh 12 × 30 (1.14) 0.081mm

Throughout testing the influent water temperature was maintained at 54°F. (12° C.). The MIB concentration in tests was based on the highestlevel experienced at the treatment plant during a taste and odorepisode. Performance in the RSSCTs thus indicates the GACs' ability toperform under strained conditions. The natural organic matter content ofthe test sample was about 3.0 mg/L, measured as total organic carbon(TOC).

Performance was measured in terms of simulated service time provideduntil the effluent reached the human odor threshold of 14 ng/L. FIG. 4presents breakthrough data of 2-methylisoborneol as simulated in RSSCTs.Values shown with arrows indicate number of service days until effluentconcentration exceeds odor threshold of 14 ng/L. Both mesoporus coconutshell-based GACs in accordance with one or more embodiments providedabout 53 days of service time until reaching this threshold. Thebituminous coal-based GACs provided about 16 to about 23 days of servicetime. The typical virgin coconut shell-based GAC provided 8 days ofservice time. The data indicates that mesoporous coconut shell-basedGACs in accordance with one or more embodiments would allow the utilityto reach almost two months of service time during a taste and odorevent.

Example 5

RSSCTs were conducted to determine the effectiveness and efficiency oftypical virgin coconut shell-based GAC versus mesoporous coconutshell-based GAC for removing a select set of chlorinated organiccompounds. These compounds had been identified historically in agroundwater source. Tetrachloroethylene (PCE), carbon tetrachloride(CTC), and 1,2,3-trichloropropane (TCP) were dosed to historicalconcentrations; trichloroethylene (TCE) and chloroform were present inthe as-received water and were not dosed additionally. Chloroform wasapparently present only in the post-spike (i.e. test influent) water; itmay have been present in the as-received water however preliminarytesting did not screen for this compound.

Compounds Examined in RSSCTs:

As-Filtered Water Avg. Post-Spiking for Compound for RSSCT (ug/L) RSSCT(ug/L) carbon tetrachloride (CTC) 1.4 2.7 tetrachloroethylene (PCE) 1.95.2 1,2,3-trichloropropane (TCP) 0.17 0.410 trichloroethylene (TCE) 1.81.5 chloroform — 0.67

Testing was conducted according to ASTM Standard Test Method D-6586-03,the Prediction of Contaminant Adsorption on GAC in Aqueous Systems UsingRapid Small-Scale Column Tests. RSSCT columns were designed to simulatethe full-scale operation of a single 12 foot diameter, 30,000 lb GACadsorber at 1000 gpm. Small-scale columns were constructed ofpolycarbonate with stainless steel fittings, PTFE tubing, and stainlesssteel influent vessels.

Vessel/Column Operating Parameters:

Full-Scale Small-Scale Flow Rate 1000 gpm 23.9 mL/min Fill Weight 30,000Lb 0.518 g Bed Depth (varies w/AD) 10.5 ft 6.0 cm Bed/Column Diameter 12ft 0.48 cm Hydraulic Loading Rate 8.8 gpm/ft² 33 gpm/ft² Particle Size12 × 30 US Mesh 170 × 200 US Mesh

To best replicate the conditions that would be observed on site (e.g.background organics) the RSSCTs were conducted with a sample of thenatural water. To prepare this water for the RSSCTs it was filteredthrough a 0.2 μm absolute-rate Flotrex cartridge (Osmonics, Inc.) toremove any suspended solids. Thereafter, contaminants were spikedconcurrently using standard mixtures (5000 μg/mL) of the compoundsdissolved in methanol (Supelco, Bellefonte, Pa.). After spiking thefiltered site water with the target contaminants, the water was held atabout 2 to about 4° C. for the duration of the test and kept under about4 psi of nitrogen gas. This procedure aimed to minimize thevolatilization of the contaminants during the about 48 hour RSSCTduration.

Influent and effluent samples were analyzed according to the CaliforniaDepartment of Public Health Modified USEPA Method 524.2 for TCP and bythe standard USEPA Method 524.2 for all other chlorinated organics. Bythis approach reporting limits for TCP analysis were 0.005 μL and 0.5μg/L for CTC, PCE, TCE, and chloroform.

The RSSCTs simulated the contaminant removal that would be observed atup to 370 days of service time. FIG. 5 presents breakthrough data ofchloroform from groundwater as measured in RSSCTs. During this periodonly chloroform breakthrough was observed above the method detectionlimit (MDL). For virgin coconut shell-based GAC, chloroform was detectedat 160 days of service life. For mesoporous coconut shell-based GAC inaccordance with one or more embodiments, chloroform was detected at 250days of service life. This represents a 56% improvement in service lifeto detection.

Example 6

RSSCTs were conducted to measure the performance of mesoporous coconutshell-based GAC and virgin coconut shell-based GAC 1230C (AC1230C),versus a reagglomerated bituminous coal-based GAC. The compounds ofinterest for this testing were a select set of chlorinated organics andthese had been identified historically in the influent groundwater atthe site.

Compounds Examined in RSSCTs

As-Filtered Water for Average Post- RSSCT Spiking for Compound (ug/L)RSSCT (ug/L) 1,1-dichloroethene (1,1-DCE) 0.99 1.81 1,1-dichloroethane(1,1-DCA) 3.21 3.74 cis-1,2-dichloroethene (cis-1,2-DCE) 0.25 1.131,1,1-trichloroethane (1,1,1-TCA) 0.70 0.92 Trichloroethene (TCE) 1.9410.38 Tetrachloroethene (PCE) 0.62 0.62

Testing was conducted according to ASTM Standard Test Method D-6586-03,the Prediction of Contaminant Adsorption on GAC in Aqueous Systems UsingRapid Small-Scale Column Tests. RSSCT columns were designed to simulatethe full-scale operation of the existing vessels. Columns wereconstructed of polycarbonate with stainless steel fittings, PTFE tubing,and stainless steel influent vessels.

Vessel/Column Operating Parameters:

Full-Scale Small-Scale Flow Rate 510 gpm about 58 mL/min Fill Weight17,000 Lb 1.68 g Bed Depth 7.1 ft 17.5 cm Column Diameter 10 ft 0.48 cmHydraulic Loading Rate 6.5 gpm/ft² 80 gpm/ft² Particle Size 12 × 40 USMesh 170 × 200 US Mesh

RSSCTs were conducted with a sample of groundwater obtained directlyfrom a municipal well. In preparation for the RSSCT this water waspassed through a 0.2 μm. Flotrex filter (Osmonics, Inc.) to remove anysuspended solids. The contaminants were spiked to representativeconcentrations using standard mixtures (1000-5000 μg/mL) of the 5 targetcompounds dissolved in methanol (Supelco, Bellefonte, Pa.). Afterspiking the filtered site water with the target contaminants, the waterwas held at 4° C. for the duration of the test and kept under about 5psi of nitrogen gas. Effluent temperature for both columns wasconsistently about 13° C. to about 14° C.

Influent and effluent samples were analyzed according to USEPA Method524.2 for volatile organic compounds. By this approach detection limitswere 0.3-0.5 μg/L. The background TOC concentration of the as-receivedgroundwater was also measured and the average of 5 samples was 0.2 mg/L.

The RSSCTs for virgin coconut and virgin bituminous were able tosimulate full-scale results that would be observed at up to 180 days ofservice time. The RSSCT for mesoporous coconut was extended to simulate330 days of service time as breakthrough did not begin to occur untilabout 180 days. During this period, only breakthrough of 1,1-DCA wasobserved. The breakthrough of other influent contaminants was notobserved during this period and all concentrations were non-detect ineffluent samples.

Initial breakthrough (above the detection limit of 0.4 μg/L) for virginbituminous occurred at 11,800 bed volumes (BV) and breakthroughcontinued steadily thereafter, reaching 95% of the influentconcentration by about 31,000 BY. For virgin coconut breakthrough wasfirst observed with the sample at 23,500 BV and by about 31,000 BVbreakthrough had reached 42% of the influent concentration. Breakthroughwas first observed with mesoporous coconut at about 32,000 BV andreached 75% of the influent concentration at about 53,000 BY.

By fitting a mathematical curve to the data points (gray short-dashedlines) the length of each mass transfer zone (MTZ) could be calculatedas described in the ASTM RSSCT method. As such, the expected full-scaleMTZ length for mesoporous coconut would be 3.2 feet versus a length of3.8 feet for virgin coconut and 4.5 feet for virgin bituminous. The MTZlength of mesoporous coconut indicates the adsorption rate was about 30%faster than virgin bituminous during adsorption of 1,1-DCA.

FIG. 6 presents breakthrough data of 1,1-dichloroethane (1,1-DCA) versusbed volumes as measured in RSSCT comparing Mesoporous Coconut and VirginCoconut to reagglomerated Virgin Bituminous GAC. Data was used toestimate a full shape of the breakthrough curve (short dashed lines).Detection limit for 1,1-DCA is also shown (long dashed lines). Datapoints shown in white were non-detect at this limit.

From the fit curve it could be estimated also that breakthrough of 0.4mg/L 1,1-DCA occurred at about 10,000 BV for virgin bituminous, about19,700 BV for virgin coconut, and about 29,400 BV for mesoporouscoconut. As a general conclusion, when applied at a full-scale about 8.2minute empty-bed contact time mesoporous coconut would be expected toprovide 167 days of service life to breakthrough of 1,1-DCA. Under thesame conditions, virgin coconut would be expected to provide 112 days ofservice life, and virgin bituminous 57 days of service life. Thereforethe use of mesoporous coconut would provide a about 200% improvement inbed life over virgin bituminous and about 50% improvement over virgincoal.

Example 7

A target application is removal of pesticides from water and as suchethylene dibromide (EDB) can be used to represent the larger class ofhalogenated pesticide compounds. RSSCTs (ASTM D6586) were performed toassess EDB removal performance of the GAC produced in accordance withone or more of the disclosed embodiments. For these RSSCTs, EDB wasspiked to a level of 300 ng/L in a natural groundwater supply, RSSCTswere scaled to represent a full-scale bed operating at a 5 minuteempty-bed contact time using 12×40 US mesh full-size grains. EffluentEDB concentrations were measured for about 70,000 bed volumes,corresponding to approximately 8 months of full-scale service.

FIG. 7 presents ethylene dibromide breakthrough data in the groundwateras measured in RSSCTs. The results indicate that the mesoporousactivated carbon produced in accordance with one or more embodimentsprovided 90% longer bed life (59,000 bed volumes) to 50% breakthroughthan the virgin material (31,000 bed volumes) and about 50% longer bedlife (39,000 bed volumes) than the bituminous product in a naturalgroundwater containing competing background organics at a level of 0.5mg/L TOC.

Example 8

A set of RSSCTs was conducted with surface water to compare totalorganic carbon (TOC) removal between the reactivated bituminous-basedgranular activated carbon (GAC) and reactivated mesoporous coconutshell-based GAC. These tests simulated the full-scale operation ofexisting GAC vessels. RSSCT test operation was based on ASTM MethodD-6586 and modified for proportional diffusivity scaling which appliesto simulating the removal of large organic compounds. Influent andeffluent samples were analyzed for total organic carbon (TOC)concentration.

Full-Scale dimensions and operating parameters that were simulated inthe RSSCTs:

Reactivated Mesoporous Reactivated Carbon Type Coconut Bituminous GrainSize 12 × 30 8 × 30 US Mesh Apparent Density 0.47 0.53 g/mL BackwashedDensity 0.43 0.49 g/mL Weight/Adsorber 35,500 40,000 lb AdsorberDiameter 12 ft Flow/Train 46.3 gpm Area 113 sq ft gpm/sq HydraulicLoading 4.1 ft Empty-Bed Contact 23.7 min Time

Small-Scale dimensions and operating parameters of RSSCTs:

Reactivated Mesoporous Reactivated Carbon Type Coconut Bituminous GrainSize 200 × 400 US Mesh Bed Depth 11.4 8.8 cm Bed Volume 2.0 1.6 mLWeight/Column 0.91 0.85 g Flow 2.0 mL/min Column Diameter 0.48 cm EBCT1.02 0.78 min

FIG. 8 presents breakthrough data of organic compounds measured as TotalOrganic Carbon (TOC) in the surface water as measured in RSSCTs.Reactivated mesoporous coconut provided about 7 days longer service lifeto an effluent of about 1.5 ppm TOC. Above 1.5 ppm, the reactivatedmesoporous coconut matches the performance of reactivated bituminous. Atypical coconut shell-based GAC would be expected to show near-immediateTOC breakthrough due to its solely microporous nature.

Having now described some illustrative embodiments, it should beapparent to those skilled in the art that the foregoing is merelyillustrative and not limiting, having been presented by way of exampleonly. Numerous modifications and other embodiments are within the scopeof one of ordinary skill in the art and are contemplated as fallingwithin the scope of the invention. In particular, although many of theexamples presented herein involve specific combinations of method actsor system elements, it should be understood that those acts and thoseelements may be combined in other ways to accomplish the sameobjectives.

It is to be appreciated that embodiments of the devices, systems andmethods discussed herein are not limited in application to the detailsof construction and the arrangement of components set forth in thefollowing description or illustrated in the accompanying drawings. Thedevices, systems and methods are capable of implementation in otherembodiments and of being practiced or of being carried out in variousways. Examples of specific implementations are provided herein forillustrative purposes only and are not intended to be limiting. Inparticular, acts, elements and features discussed in connection with anyone or more embodiments are not intended to be excluded from a similarrole in any other embodiments.

Those skilled in the art should appreciate that the parameters andconfigurations described herein are exemplary and that actual parametersand/or configurations will depend on the specific application in whichthe systems and techniques of the invention are used, Those skilled inthe art should also recognize or be able to ascertain, using no morethan routine experimentation, equivalents to the specific embodiments ofthe invention. It is therefore to be understood that the embodimentsdescribed herein are presented by way of example only and that, withinthe scope of the appended claims and equivalents thereto; the inventionmay be practiced otherwise than as specifically described.

Moreover, it should also be appreciated that the invention is directedto each feature, system, subsystem, or technique described herein andany combination of two or more features, systems, subsystems, ortechniques described herein and any combination of two or more features,systems, subsystems, and/or methods, if such features, systems,subsystems, and techniques are not mutually inconsistent, is consideredto be within the scope of the invention as embodied in the claims.Further, acts, elements, and features discussed only in connection withone embodiment are not intended to be excluded from a similar role inother embodiments.

The phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. As used herein, theterm “plurality” refers to two or more items or components. The terms“comprising,” “including,” “carrying,” “having,” “containing,” and“involving,” whether in the written description or the claims and thelike, are open-ended terms, i.e., to mean “including but not limitedto.” Thus, the use of such terms is meant to encompass the items listedthereafter, and equivalents thereof, as well as additional items. Onlythe transitional phrases “consisting of” and “consisting essentiallyof,” are closed or semi-closed transitional phrases, respectively, withrespect to the claims. Use of ordinal terms such as “first,” “second,”“third,” and the like in the claims to modify a claim element does notby itself connote any priority, precedence, or order of one claimelement over another or the temporal order in which acts of a method areperformed, but are used merely as labels to distinguish one claimelement having a certain name from another element having a same name(but for use of the ordinal term) to distinguish the claim elements.

What is claimed is:
 1. A method of producing an enhanced activatedcarbon, comprising: providing a predominantly microporous virginactivated carbon; introducing an aqueous calcium-based catalyst to thevirgin activated carbon to produce a catalyst impregnated activatedcarbon; and heating the catalyst impregnated activated carbon at apyrolysis temperature until a mesopore volume of at least about 10% isachieved while substantially maintaining a micropore structureassociated with the virgin activated carbon to produce the enhancedactivated carbon.
 2. The method of claim 1, wherein the method isassociated with a mass loss of at least about 10%.
 3. The method ofclaim 1, wherein the aqueous calcium-based catalyst comprises calciumchloride.
 4. The method of claim 1, wherein the aqueous calcium-basedcatalyst comprises a chelator.
 5. The method of claim 4, wherein thechelator comprises citric acid.
 6. The method of claim 1, wherein thevirgin activated carbon is coconut shell-based.
 7. The method of claim1, wherein the virgin activated carbon is at least about 90%microporous.
 8. The method of claim 1, wherein the catalyst impregnatedactivated carbon is maintained at an intermediate temperature prior toreaching the pyrolysis temperature.
 9. The method of claim 1, whereinthe virgin activated carbon is sprayed with or soaked in the aqueouscalcium-based catalyst.
 10. The method of claim 1, further comprisingoxidizing the catalyst impregnated activated carbon with carbon dioxide.11. The method of claim 10, wherein the catalyst impregnated activatedcarbon is oxidized with carbon dioxide and steam.
 12. A method ofproducing an enhanced activated carbon, comprising: providing a spentactivated carbon having a calcium content of greater than or equal toabout 0.5% by weight; and heating the spent activated carbon to apyrolysis temperature until a mesopore volume of at least about 10% isachieved to produce the enhanced activated carbon.
 13. The method ofclaim 12, wherein the spent activated carbon is predominantlymicroporous.
 14. The method of claim 12, wherein the spent activatedcarbon is coconut shell-based.
 15. The method of claim 12, furthercomprising oxidizing the spent activated carbon with at least one ofcarbon dioxide and steam.
 16. A method of facilitating water treatment,comprising: providing a vessel containing coconut shell-based activatedcarbon having a mesopore volume of at least about 10%; and fluidlyconnecting a source of water to the reactor for treatment via contactwith the coconut shell-based activated carbon.
 17. The method of claim14, further comprising reactivating the coconut shell-based activatedcarbon after a predetermined time period. 18-20. (canceled)